Update minimum version of symfony/yaml to 2.0.5 (#268)
Update minimum version of symfony/yaml to 2.0.5 (#268)

I'm using `php-coveralls` with `composer update --prefer-lowest` as part of my test matrix.

With 2.0.0 - 2.0.4, I get the error:

```
Error: Class 'Symfony\Component\Yaml\Parser' not found in /Users/gr4376/Projects/lib-gedcom/vendor/php-coveralls/php-coveralls/src/Bundle/CoverallsBundle/Config/Configurator.php on line 56
```

With 2.0.5, `php-coveralls` runs as expected.
php-coveralls/php-coveralls